The principal attraction of the locality is what has come to be called the _Firehole_. It is at the extreme upper end of the valley, difficult to find, and unsatisfactory to visit when the wind agitates the water surface. It is a large hot spring from the bottom of which, to all appearances, a light colored flame is constantly issuing, only to be extinguished in the water before it reaches the surface. At times it has a distinct ruddy tinge and it always flickers back and forth like the lambent flame of a torch. When seen under favorable conditions, the illusion is perfect, and the beholder is sure that he has at last caught a glimpse of the hidden fires which produce the weird phenomena of this region. But it is only illusion. Through a fissure in the rock gas or superheated steam escapes and divides the water, just as bubbles do on a smaller scale. The reflection from the surface thus formed accounts for the appearance, which is intensified by the black background formed by the sides and bottom of the pool. The Lower Geyser Basin has an area of thirty square miles. Conspicuous among its topographical features are the _Twin Buttes_, two prominent peaks west of the river which dominate the entire basin. A little way south of these is _Fairy Fall_, a pretty cascade 250 feet high. There will be included in this chapter, as more properly belonging to it than to the next, a description of the _Midway Geyser Basin_. Its principal interest lies in the stupendous character of its phenomena. [Illustration: _Terry Engr. Co._ _Haynes, Photo., St. Paul._ Excelsior Geyser.] _Excelsior Geyser_, as a dynamic agent, has no equal in the Park. It is really a water volcano, and its eruptions have nothing of the characteristic display of a genuine geyser. Its crater is a vast seething cauldron close by the brink of the Firehole River, into which, in non-eruptive periods even, it pours 4,000 gallons of water per minute. The shape of the crater is irregular. Its dimensions are about 330 by 200 feet, and 20 feet deep. It was not known to be a geyser until 1878, and did not really disclose its true character until the winter of 1881. During the remainder of that year and 1882, it gave continuous exhibitions of its power. Its water column was more than 50 feet in diameter, and at times rose to the enormous height of 250 feet. At such times, it doubled the volume of water in the Firehole River. Its eruptions were frequently accompanied by the ejection of large rocks. A second period of activity took place in 1888, since which time it has remained inactive.